Alloy steels



June 1964 o. HARDWICK ETAL 3,135,600

ALLOY STEEL-S Filed March 13, 1962 0 C 0 Fv i G E E R \H m mm M E mph 3w M A F. F T 0T m 2m W. .w. m w w w v w 0 0 o.

/n um in I: 120/: aid Hare/wick United States Patent 3,135,600 ALLQYSTEELE) Donald Hardwiclk, Totley, Shefiield, and Henry William Kirlrby,Totiey Rise, Shehicld, England, assignors to Thos. Firth 8; john BrownLimited, Sheffieid, England, a British company Filed Mar. 13, 1962, Ser.No. 179,399 Claims priority, application Great Britain Mar. 15, 1961Claims. (Cl. 75-128) The invention relates to alloy steels. Theinvention provides in one of its aspects an alloy steel having thefollowing composition.

Carbon ODS-0.30%.

Silicon Not more than 0.35% Manganese 0.60-0.80%.

Nickel 8.00-9.00%. Chromium 0.25-l.5%. Molybdenum 0.30-

Substantial remainder apart Iron from usual impurities.

The alloy steel provided by the invention has high hardenability. Itpossesses good low temperature impact properties at high tensile levelswhen formed into articles of thick section.

This steel is particularly applicable to the manufacture of large hightensile turbine wheels for turbo-alternator plant, although it may beused for rotor shafts and other components where low transitiontemperatures, however defined, but normally estimated from notchedimpact tests carried out over a range of temperatures, are necessary ordesirable. Above the transition temperature, fractures are predominantlyductile, but below the transition temperature there is an increasingtendency tobrittle fracture. Good low temperature impact propertiesimply a low transition temperature.

The normal alloy steels used for the applications mentioned above sufferfrom the disadvantage that as the tensile level increases above 60-65tons/in. (ultimate tensile strength) the transition temperatures becomeunacceptably high. It has now been found that by addition of certainamounts of chromium and molybdenum to certain nickel steels, an alloy isobtained having improved low temperature impact properties at tensilelevels of 60-100 tons/in. (ultimate tensile strength), after heattreatments consisting preferably of tempering following slow coolingfrom austenitizing temperature.

Following is a description by way of example only of methods of carryingthe invention into effect.

EXAMPLE 1 A bar 4 inch in diameter was formed from an alloy steelaccording to the invention having the following composition:

Carbon 0.18%.

Silicon 0.30%.

Manganese 0.76%.

Nickel 8.40%.

Chromium 0.99%.

Molybdenum 0.51%.

Iron Substantial remainder apart from usual impurities.

Portions of this bar were subjected to the following three heattreatments.

No. 1.The bar was austenitized at a temperature of 900 C. for /2 hour,cooled to room temperature at a rate of 10 C./hour, tempered at 600 C.for one hour and then water quenched.

No. 2.-The sample was austenitized at a temperature of 900 C. for /2hour and then air-cooled to 200 C. at

3,135,600 Patented June 2, 1964 which temperature the sample wasmaintained for one hour. The sample bar was then tempered at 600 C. forfour hours and finally water quenched.

No. 3.--The sample was austenitized at 900 C. for /2 hour and then aircooled to 200 C.,'the temperature of the bar being maintained at 200 C.for one hour. The sample was then air-cooled to room temperature.

The properties of the bore resulting fromthese heat treatments are givenin the following tables.

Charpy V Notch Value, ft. lb.

Test Temp, 0.

Heat Treat- Heat Treat- Heat Treatment 3 ment 1 ment 2 EXAMPLE 2 A /1bar was formed from an alloy steel according to the invention having thecomposition:

Balance Iron.

Portions of this bar were subjected to the following four heattreatments.

N0. 4.--The sample was austenitized at 830 C. for /2 hour, air cooled toroom temperature, tempered at 600 C. for 4 hours and then waterquenched.

No. 5.The sample bar was austenitized at 830 C. for /2 hour, air cooledto room temperature, tempered at 600 C. for 4 hours and then cooled toroom temperature at a rate of 10 C. per hour.

No. 6.The bar was austenitized at 830 C. for /2 hour, air-cooled to roomtemperature, tempered at 500 C. for 4 hours and then water-quenched.

N0. 7.--A. sample of the bar was austenitized at 830 C. for /2 hour,air-cooled to room temperature, tempered at 500 C. for 4 hours and thencooled to room temperature at a rate of 10 C. per hour.

The properties of the bars resulting from these heat treatments aregiven in the following tables.

Mechanical Properties 0.5% Ultimate Elonga- Reduction Heat Treatment No.Proof Tensile tion, in Area, Stress Strength percent percent A l-toncast of alloy steel was made according to the invention having thefollowing composition:

Carbon 0.21%. Silicon 0.23%. Manganese 0.67%. Nickel 8.55%. Chromium0.92%. Molybdenum 0.93%. Iron Substantial remainder apart from usualimpurities.

From this cast, /8 inch Gothic bar and 6 inch diameter billet wereprepared. Portions of the bar were subjected to the followingheat-treatments.

N0. 8.The bar was austenitized at a temperature of 850 C. for /2 hour,air cooled to room temperature and tempered at various temperatures upto 625 C. After tempering, the samples were water-quenched.

N0. 9.The bar was austenitized at a temperature of 850 C. for /2 hourand cooled to room temperature at C./hour.

T empering was carried out at various temperatures in the range 450625C. After tempering the samples were water quenched.

The properties of the bars resulting from these heattreatments aregraphically illustrated in FIGURE 2. In this graph, curve A is a plot ofCharpy V-notch values in ft. lbs. in a tangential direction against theTest Temperature in C., and curve B is a plot of Charpy V-notch valuesin ft. lbs., in an axial direction, against the Test Temperature. Bothin tensile properties and in room temperature Charpy V-notch impacttests, there is little difference between specimens air-cooled or slowlycooled after tempering.

When a steel is to be used in massive sections, it is desirable toensure the formation of the required transformation product on coolingfrom the austenitizing temperature; this is done by cooling at such arate that residual stresses are introduced into the section. Thetempering temperature then has to be such that these stresses relaxduring tempering. With the alloy steel provided by the invention, thehigh hardenability makes it possible to use a slow cooling rate from theaustenitizing temperature. The residual stresses remaining in thesection are therefore negligible, tempering may be carried out at a lowtemperature. In pursuance of this idea, a disc 12 inches in diameter and5 inches thick was pro duced by upsetting a suitable length from the 6inch diameter billet. This disc was subjected to the following heattreatment.

No. 10.The disc was austenitized at a temperature of 830 C. for 1 hourand cooled to room temperature at 10 C./hour. Tempering was carried outat 300 C. for 4 hours, followed by cooling at 10 C./hour to roomtemperature.

Axial and tangential specimens were cut from the disc after heattreatment, and the various mechanical properties of these specimens aregraphically illustrated in FIG- URE 1. In this graph, curve C is a plotof Charpy V-notch values in ft. lbs. against Tempering Temperature C.)on a specimen cooled at a rate of 10 per hour. from 850 C., and curve Dis a similar plot for a specimen air cooled from 850 C. Curve E is aplot of the 0.2% proof stress in tons/sq. in. against TemperingTemperature C.) on a specimen cooled at a rate of 10 per hour from 850C., and curve F is a similar plot for a specimen air cooled from 850 C.Curve G is a plot of maximum stress in tons/sq. in., against temperingtemperature C.) on a specimen cooled at a rate of 10 per hour from 850C., and curve H is a similar plot for a specimen air-cooled from 850 C.

0.5% Ultimate Reduc- Heat Test proof tensile Elongation in TreatmentPosition stress, strength, tion, Area,

No. tons/ tons/ percent percent sq. 111. sq. in.

10 Axial 85.6 90.8 7 20 TangentiaL. 70. 0 90. 2 10 46 Thus, by means ofa low'temperature tempering treatment, an attractive combination of hightensile strength, ductility and low temperature properties may beobtained in the steel of this invention.

We claim:

1. A high hardenability alloy steel having the following criticallybalanced composition:

Carbon 0.05-0.30%. Silicon Up to a maximum of 0.35%. Manganese 0.60 to0.80%. Nickel 8.00 to 9.00%. Chromium 0.25 to 1.50%.

and Molybdenum 0.30 to 1.50%.

the remainder being substantially iron with the usual impurities inordinary amounts.

2. A high hardenability alloy steel having the following criticallybalanced composition:

Percent Carbon About 0.18 Silicon About 0.30 Manganese About 0.76 NickelAbout 8.40 Chromium About 0.99

and

Molybdenum About 0.51

the remainder being iron with the usual impurities in ordinary amounts.

3. A high hardenability alloy steel having the following criticallybalanced composition:

Percent Carbon About 0.19 Silicon About 0.13 Manganese About 0.68 NickelAbout 8.33 Chromium About 0.97

and

Molybdenum About 1.02

the remainder being iron with the usual impurities in ordinary amounts.

4. A high hardenability alloy steel having the following criticallybalanced composition:

the remainder being iron with the usual ordinary amounts.

5. A process for the manufacture of a high hardenimpurities in abilityalloy steel, which process comprises making an alloy having thefollowing composition:

heating the alloy within the range 800 C. to 950 C., 10 cooling thealloy at a maximum rate of 10 C. per hour to a temperature Within therange 0 C. to 250 C., heating the alloy at a temperature of 300 C. to650 C. and subsequently cooling to room temperature.

References Cited in the file of this patent UNITED STATES PATENTS BagsarAug. 24, 1943 Brophy et a1 Oct. 19, 1948 Newell Nov. 28, 1950 KorczynskyJune 25, 1957 Hodge et a1. July 9, 1957 Yeo et a1 July 11, 1961 OTHERREFERENCES The Metals Handbook, 1948 edition, article on page

1. A HIGH HARDENABILITY ALLOY STEEL HAVING THE FOLLOWING CRITICALLYBALANCED COMPOSITION: